1. Field of the Invention
This invention relates to a semiconductor device and a manufacturing method thereof, particularly, to a semiconductor device having a semiconductor substrate formed with a via hole and a manufacturing method thereof.
2. Description of the Related Art
Conventionally, a BGA (ball grip array) type semiconductor devices have been known as a kind of a chip size package having almost same outside dimensions as those of a semiconductor die. In this BGA type semiconductor device, a plurality of ball-shaped terminals made of a metal such as solder is arrayed in a grid pattern on one surface of the package, and electrically connected with the semiconductor die mounted on the other side of the package.
When this BGA type semiconductor device is mounted on electronic equipment, the semiconductor die is electrically connected with an external circuit on a printed circuit board by compression bonding of the ball-shaped terminals to wiring patterns on the printed circuit board.
Such a BGA type semiconductor device has advantages in providing a large number of ball-shaped terminals and in reducing size over other CSP type semiconductor devices such as SOP (Small Outline Package) and QFP (Quad Flat Package), which have lead pins protruding from their sides. The BGA type semiconductor device is used as an image sensor chip for a digital camera incorporated into a mobile telephone, for example. In this case, a supporting substrate made of, for example, glass is attached to a surface or both surfaces of the semiconductor die. The relating technology is disclosed in the Japanese Patent Application Publication No. 2002-512436.
Next, descriptions will be made on the BGA type semiconductor device and the manufacturing method thereof of the conventional art in a case where a sheet of supporting substrate is attached to the semiconductor die, with reference to drawings.
FIGS. 5 to 7 are cross-sectional views of the BGA type semiconductor device and the manufacturing method thereof of the conventional art, which are applicable to the image sensor chip. First, as shown in FIG. 5, a pad electrode layer 34 made of an aluminum layer or an aluminum alloy layer is formed on a top surface of a semiconductor substrate 30 with an insulation film, for example, an oxide film 31 interposed therebetween. Then, a supporting substrate 36 made of, for example, a glass is further attached on the top surface of the semiconductor substrate 30 including the pad electrode layer 34 with a resin layer 35 interposed therebetween.
Next, as shown in FIG. 6, a resist layer 37 is formed on a back surface of the semiconductor substrate 30, having an opening in a position corresponding to the pad electrode layer 34. Then, dry etching is performed to the semiconductor substrate 30 by using this resist layer 37 as a mask to form a via hole 38 from the back surface of the semiconductor substrate 30 to the pad electrode layer 34. On a part of the pad electrode layer 34 at a bottom of the via hole 38 formed by the etching, an aluminum oxide 50 (e.g. Al2O3 compound) is formed during etching.
Then, as shown in FIG. 7, a barrier layer 39 is formed on the back surface of the semiconductor substrate 30 including inside the via hole 38. A seed layer for plating 40 is formed on the barrier layer 39, and plating is performed to this seed layer 40 to form a re-distribution layer 41 made of, for example, copper (Cu). Furthermore, a protection layer (not shown) is formed on the re-distribution layer 41, and an opening is formed in a predetermined position of the protection layer to form a ball-shaped terminal 42 being in contact with the re-distribution layer 41.
Then, although not shown, the semiconductor substrate and the layers laminated thereon are cut off and separated into individual semiconductor dice. In this way, the BGA type semiconductor device where the pad electrode layer 34 and the ball-shaped terminal 42 are electrically connected with each other is formed.
However, when the via hole 38 is formed by the etching, the aluminum oxide 50 formed on the bottom thereof is positioned on a part of the pad electrode layer 34, thereby forming high resistance between the pad electrode layer 34 and the re-distribution layer 41. Furthermore, the aluminum oxide 50 degrades covering characteristics of the pad electrode layer 34 for the re-distribution layer 41, thereby easily causing damages such as disconnection of the re-distribution layer 41. This causes a problem of deteriorating the characteristics of the semiconductor device.
Although this problem seems to be solved by removing this aluminum oxide 50 by further etching, the etching process adds to the complexity of the manufacturing process.